How drugs act and interact, how they enter the body, what happens to them inside the body, how they are eliminated from it; the effects of genetics, age, and disease on drug action — these topics are important for, although they will generally not be in the front of the conscious mind of the prescriber,an understanding of them will enhance rational decision taking.
Knowledge of the requirements for success and the explanations for failure and for adverse events will enable the doctor to maximise the benefits and minimise the risks of drug therapy.
• Qualitative aspects; Receptors, Enzymes, Selectivity
• Quantitative aspects: Dose response, Potency, Therapeutic efficacy.Tolerance
• Time course of drug concentration: Drug passage across cell membranes; Order of reaction; Plasma half-life and steady-state concentration; Therapeutic drug monitoring
• Individual processes: Absorption, Distribution, Metabolism, Elimination
• Drug dosage: Dosing schedules
• Chronic pharmacology: the consequences of prolonged drug administration and drug discontinuation syndromes
• Individual or biological variation: Variability due to inherited influences, environmental and host influences
• Drug interactions: outside the body, at site of absorption, during distribution, directly on receptors, during metabolism, during excretion
Pharmacodynamics is what drugs do to the bod/: pharmacokinetics is what the body does to drugs.
It is self-evident that knowledge of pharmacodynamics is essential to the choice of drug therapy. But the well-chosen drug may fail to produce benefit or may be poisonous because too little or too much is present at the site of action for too short or too long a time. Drug therapy can fail for pharmacokinetic as well as for pharmacodynamic reasons. The practice of drug therapy entails more than remembering an apparently arbitrary list of actions or indications.
Technical incompetence in the modern doctor is inexcusable and technical competence and a humane approach are not incompatible as is sometimes suggested.
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